The present disclosure relates to a secure electronic structure, an integrated circuit which includes the secure electronic structure and a method of forming the same. More particularly, the present disclosure relates to an electronic structure containing sub-lithographic random conductors as a physical unclonable function or PUF.
In the electronics industry, security in an electronic device has become a major concern of manufacturers and users of such devices. In this regard, it is useful to be able to distinguish each electronic device, especially the integrated circuit (IC) within these devices, from each other. This is particularly true for devices such as computers, personal hand held devices, cellular phones, chip cards, and other devices that contain sensitive information. Developers of electronic devices continuously strive to provide systems and methods that make their products impervious to unauthorized access or use. Communication devices used in the military and security fields are one category of devices that must remain secure despite physical and electrical tampering, while other categories also require this feature.
At the same time, most applications have cost limitations that must be taken into account. For example, if a complicated authentication process requiring storage and computing resources were employed on an integrated circuit, the costs incurred may not justify the cost of security accomplished, particularly if the end product were a low cost and mass produced consumer product.
One approach to solve the above identified problems is to employ a physical unclonable function (PUF) to provide a unique, secure bit, word or function for use in generating security keys. A PUF may eliminate the need for storage of a public or private key on a device. PUFs are known in the art to be implemented by circuits, components, processes or other entities capable of generating an output, such as a digital bit, word or a function that is resistant to cloning.
Typically, the PUF can be generated based on inherent physical characteristics of a device such as, for example, individual physical characteristics of a transistor such as a threshold voltage of the transistor which varies due to local process variations during manufacturing. There is no need to store the PUF within the device, because the PUF can be generated repeatedly. Moreover, it is nearly impossible to clone a device having a PUF implemented in a manner to generate the same PUF output with another device.
Although PUFs have been implemented within electronic devices and secure IC's, there exists a need to create an electronic structure having a physical unclonable function embodied in the physical structure, which is easy to evaluate but hard to predict, and which is formed using standard integrated circuit manufacturing methods and materials. It is desirable to fabricate the PUF during standard integrated circuit manufacturing and to add a minimum number of additional process steps in order to complete the PUF structure.
There are special applications of a PUF structure in which a secure integrated circuit must remain secure requiring destruction or erasure of the information stored in the PUF, and it is desirable for destruction or erasure to be rapid and easily triggered by an electrical pulse. Thus, a PUF that is quickly erased is needed in special secure IC's.
In present and future IC's another aspect that is desirable is fabrication of a PUF that is as small as possible, thus using a minimum amount of area of the IC or chip. Construction of a very small PUF structure with a minimum area is facilitated using sub-lithographic dimensions, and there exists a need for a PUF in which the patterned dimensions are less than about 40 to 50 nm, and in which a lithographic patterning step is avoided during fabrication in order to generate the random pattern for the PUF element, and to reduce fabrication costs.